Atrial Fibrillation

Today we talked about atrial fibrillation in a patient with a history of rheumatic fever. On GIM, atrial fibrillation is a diagnosis we see very commonly.

One of the best atrial fibrillation resources is the 2006 ACC/AHA Guidelines which you can find here. As a side note, the ACC/AHA have guidelines on a huge variety of cardiovascular topics that provide an evidence base for cardiac decision making on the wards. Here's the list.

Briefly about atrial fibrillation:

1. Afib is a very common arrhythmia. Seen in ~10% of patients greater than 85 years old.

2. While afib can cause distressing symptoms (palpitations, SOB, etc.), the biggest concern is thromboembolism and the impact of afib on cardiac function.

3. Generally we classify afib as:

a) paroxysmal (less than 7 days duration)

b) persistent (lasting greater than 7 days and terminating spontaneously or with cardioversion)

c) permanent (afib lasting greater than 1year and failed cardioversion/not attempted).

Regardless of the classification,

they all portend the same yearly risk of stroke.

A fourth classification is "lone atrial fibrillation" which applies to atrial fibrillation in a patient with no structural heart disease (and often less than 60 years old). These patients are generally felt to be at a low risk of stroke.

4. Most common causes of afib: HTN, valvular disease, hyperthyroidism, heart failure and alcohol.

Usually afib is not associated with stable coronary artery disease unless it results in an MI or heart failure. Afib can also be seen in the context of surgery or a pulmonary embolism.

5. Minimum set of investigations for new onset atrial fibrillation: ECG (confirm diagnosis, assess for other complicating disease), CBC, lytes, TSH and 2D Echo (to assess for structural heart disease).

6. Management consists of rate vs. rhythm control and thromboembolism risk reduction.

a) Rate vs. rhythm control:

Often a trial of cardioversion is given for the first episode of atrial fibrillation. In the long term, most patients with recurrent atrial fibrillation are managed with rate control rather than rhythm control (unless they have significant symptoms or cardiovascular compromise when in afib).

The AFFIRM Trial demonstrated that there was no survival or stroke risk advantage to a rhythm control strategy and that rhythm control more frequently resulted in medication side effects and hospitalization.

Rate control is usually accomplished with B-blockers, non-dihydropyridine calcium channel blockers (Dilt, Verapamil) or Digoxin. The guidelines suggest a HR target of less than 80bpm at rest and less than 110bpm with exercise. However, the recently published RACE-II Trial suggests that strict rate control may confer no additional benefit over lenient rate control.

b) Thromboembolism risk reduction:

The yearly risk of stroke depends on a variety of factors. Several risk scores exist, but one of the easiest to use is the CHADS2 Score. This only applies for patients with non-valvular atrial fibrillation:

Chronic Heart Failure - 1 point

HTN - 1 point

Age greater than 75 - 1 point

Diabetes - 1 point

Stroke/TIA - 2 points

If the CHADS2 score is 0 then no therapy or ASA is reasonable. With a CHADS2 score of 1 then ASA or Warfarin (INR 2-3) is acceptable and with a CHADS2 score greater than 1 warfarin is recommended.

The reason for this is that the benefit you obtain from ASA or warfarin is determined by your yearly risk of stroke. ASA provides a RRR of ~25% while warfarin gives a RRR of ~66%. The risk of a significant bleeding complication from ASA is small, while with warfarin is ~1%/year (depending on the patient).

Remember, for patients with valvular atrial fibrillation, their stroke risk is much higher (as in our patient this morning) so they should be managed with warfarin.

Interestingly, the recently published RE-LY trial showed that Dabigatran, a direct thrombin inhibitor that does not require monitoring may be superior to warfarin in terms of stroke prevention or bleeding risk (depending on the dose). This could revolutionize the way atrial fibrillation in managed.

Atrial fibrillation- acute management

Today we discussed issues related to acute management of atrial fibrillation. A few points:

After establishing that the patient's airway and breathing are stable, the first decision point is whether the patient needs emergent synched cardioversion.
Indications as per ACLS algorithm:
1) Hemodynamic instability, 2) Shock (i.e. hypoperfusion), 3) Pulmonary edema, 4) Ischemia
HOWEVER, remember that clinical judgement is absolutely required; this is not risk-free, and many patients have mild pulmonary edema and borderline hypotension with rapid A-fib and do not all need to be cardioverted.

If emergent cardioversion is indicated, important steps include
1) Consider pre-treatment with antiarrhythmic (e.g. amiodarone); increases the likelihood of success
2) Analgesia and sedation, requiring the capability to deal with the airway; usually requires the help of anesthesia unless in the ICU
3) Application of the pads- "sandwich"- front and back is more successful than sternal and lateral
4) Synchronized cardioversion with 50-100J
5) Anticoagulation for at least 4 weeks post-cardioversion

Watch for
-bradycardia (pts usually have some AV nodal agent "on board" prior that was dosed to their a-fib; if now in sinus, may be bradycardic
-embolic complications

If elective cardioversion (i.e. not emergent), considerations include
1) Embolic risk
If a-fib is present more than 48h (usually difficult to determine) or the patient was not therapeutically anticoagulated for 2 weeks or more prior, there is a significant (but difficult to quantify) risk of systemic embolization with restoration of sinus rhythm. A trans-esophageal echo that shows no evidence of a thrombus makes the risk very low, and is done in situations where emergent cardioversion is not necessary, and the above criteria are not met.
NB- the risk of embolization exists for pharmacologic cardioversion as well, although may be lower than electrical (think about this when using antiarrhythmics like amiodarone)

2) Procedural risk (sedation, analgesia, arrhythmia, etc)

If cardioversion is not indicated, rate control is the next management choice. Options include:
1) Beta-blockers (e.g. metoprolol 2.5-5mg IV over 5-10min)
2) Non-DHP calcium channel blockers (e.g. diltiazem 15-20mg IV over 5-10 min)
3) Digoxin (e.g. 0.25mg IV load)
4) Amiodarone (but note cardioversion risk as outlined above)

There is little evidence to guide us in the acute setting (but lots of evidence in the chronic setting- e.g. AFFIRM)
Reasons to use beta blockers or CCB: Little toxicity, easy to titrate, often the patient has another indication (for B-blocker), rate control is more reliable than digoxin (see below)
Reasons to think twice before using a beta blocker or CCB: LV dysfunction (esp. CCB), pulmonary edema (both), reactive airways (B-blocker), conduction system disease (both)

Reasons to consider digoxin: Is an inotrope, and carries lower risk of hypotension or worsening pulmonary edema. Works particularly well in decompensated aortic stenosis since allows more filling time without affecting contractility
Reasons to think twice before using digoxin: Patient can override it with sympathetic stimulation (that is usually present) since it does not block this, risk of toxicity if levels supratherapeutic, more difficult to use, debatable long-term benefit (definitely no mortality benefit from DIG trial)

Anticoagulation may be initiated in the ED if clearly indicated, but may also wait until the patient is more stable, and risks/benefits (which usually favour anticoagulation) have been discussed.

Who is Chad anyways?

Atrial Fibrillation. And the CHADS2 score. What's the deal?

Well, essentially this is a very simple scoring system to determine your patients risk of thromboembolism with atrial fibrillation.

• Congestive heart failure (any history): 1 point
• Hypertension (including prior history): 1 point
  
• Age > 75: 1 point
• Diabetes mellitus: 1 point
• Stroke: 2 points

Simple as that. Add up the points. A higher number of points means that the risk of thromboembolism is more likely. Low risk patients have a score of 0 - 1, where the annual incidence of stroke is less than 2.5%. A score of 2 carries a Moderate risk (4% per year) of stroke, and anything greater than 2 is High risk.

Essentially, Aspirin can be used to treat low risk patients, Aspirin or Warfarin in moderate risk patients, and Warfarin in high risk patients. Warfarin will reduce the risk of embolic stroke by about 2/3.

Here is a link to the original article published in JAMA in 2001